Carnegie stage 4

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Introduction

Week2 001 icon.jpg

Stage 4 sees the attached blastocyst begin implantation into the maternal uterine lining epithelium and underlying stroma. The entire cellular products of the original fertilisation event are now referred to as the conceptus, this will include embryonic and extra-embryonic tissues of the fetal membranes and placenta. When conceptus implantation completes, a coagulation plug is formed at the site of implantation and the entire process of development will occur enclosed within the wall of the uterus.

The process of attachment and implantation initiates the at first localised transformation of the uterine endometrium into the decidua (maternal decidua). This process is described as decidualization (decidualisation) that eventually spreads throughout the entire uterine lining.

Summary

  • Week 1-2, size 0.1 - 0.2 mm
  • Adplantation and implantation commences, increase in hCG


See also Events

Stage 4 Links: Week 2 | Implantation | | Trophoblast | Human Chorionic Gonadotropin | Lecture | Practical | Category:Carnegie Stage 4 | Next Stage 5
 
Week: 1 2 3 4 5 6 7 8
Carnegie stage: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Carnegie Stages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | About Stages | Timeline

Carnegie Collection

Note these are implanting monkey blastocysts[1] as there are no human examples of this stage in the collection.

The uterus epithelium is shown at the top of the image.

The trophectoderm (trophoblast layer proliferates and invades the epithelium.

The cytotrophoblast layer forms a squamous epithelium surrounding the blastocoel.

The inner cell mass (embryoblast) is aligned towards the epithelium.



HeuserStreeter1941 fig48.jpg


The images below are a serial serial sections of the embryo inner cell mass.

HeuserStreeter1941 fig49.jpg HeuserStreeter1941 fig50.jpg
HeuserStreeter1941 fig51.jpg HeuserStreeter1941 fig52.jpg
HeuserStreeter1941 fig53.jpg HeuserStreeter1941 fig54.jpg

Stage 4 Animation

Click Here to play on mobile device

The animation (left) shows the process of implantation, occurring during week 2 of development in humans.

The beginning of the animation shows: the uterus lining (endometrium epithelium), the hatched blastocyst with a flat outer layer of trophoblast cells (green), the inner cell mass which has formed into the bilaminar embryo (epiblast and hypoblast) and the large fluid-filled space (blastocoel).

green cells - trophoblast layer of the conceptus
blue cells - epiblast layer of the bilaminar embryo
yellow cells - hypoblast layer of the bilaminar embryo
white cells - uterine endometrium epithelium
red - maternal blood vessel (endometrial spiral arteries)


Implantation Movie Links: MP4 version | Week 2 Chorionic Cavity Movie | Implantation | Week 2 | Trophoblast | Human Chorionic Gonadotropin | Placenta Development | Movies


Week2 001 icon.jpg
 ‎‎Week 2 - Implant
Page | Play

Events

  • mitosis - cells on surface of blastocyst (trophoblast cells) divide more rapidly than the inner cells (inner cell mass, embryoblast)
  • implantation - adhesion to endometrium epithelium and implantation through this layer into the underlying uterine stroma.
  • Endocrine signalling - (hCG)trophoblast cells secrete hCG (human Chorionic Gonadotropin/Gonadotrophin) the signal of pregnancy.
  • corpus luteum - signal from trophoblasts begins to maintain this endocrine tissue in the maternal ovary that secretes progesterone.


References

Additional Images

Carnegie Stages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | About Stages | Timeline



Cite this page: Hill, M.A. (2018, September 22) Embryology Carnegie stage 4. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_4

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© Dr Mark Hill 2018, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G